The present invention relates to a lubricating oil filter for internal combustion engines, particularly of motor vehicles, with members for monitoring the degree of clogging of the filtration surface.
Internal combustion engines are provided with a forced circulation lubrication circuit the purpose of which is to maintain a lubricating oil film between all those mechanical parts undergoing relative movement, in order to reduce their friction and to remove and dissipate the heat generated.
With the passage of time, impurities accumulate in the lubricating oil, these impurities consisting mainly of metal particles deriving from the wear of the engine sliding members, carbon particles produced by the fuel and by the combustion of the seeping oil, and mineral powders, generally siliceous and calcareous, deriving from the dust suspended in the intake air.
In order to eliminate these solid particles, which with the passage of time lead to considerable wear of the moving parts of the engine, a filter cartridge in the form of a thin sheet metal casing containing a folded paper cylinder, and a valve system for controlling the passage of oil are usually provided.
These filters comprise a pressure relief valve connected as a bypass, to ensure oil feed to the engine even when the oil pressure downstream of the valve is insufficient, due either to operation at high speed or to clogging of the filter.
When this valve opens it on the one hand ensures correct lubrication, even if the filter is clogged, but on the other hand enables not only the oil but also impurities contained in it to circulate through the engine members, to produce the aforesaid damage.
It is therefore of particular importance to determine the state of clogging of the oil filter in order to be able to replace it as soon as it has exceeded its limiting operational state before the pressure relief valve is subjected to too frequent opening movements or before the oil passing through it undergoes high pressure drop, without having to rely on an estimate of average life as in the case of filters known up to the present time.